Hardy varieties of the Persian walnut are called Carpathian walnut. These varieties have characteristics that allow them to grow and produce nuts under Michigan conditions. Warm weather in early spring may break dormancy leading to flower bud kill by frosts that follow the warm spell.
Plant bare root trees in the spring. Dig a hole large enough to hold the entire root system spread out in a natural manner. Do not allow the roots to dry out during planting. Do not fertilize the first year after planting but do apply a thick mulch of hay or straw. Water each time the soil is dry through the first summer but gradually reduce watering in late August and September.
Newly planted trees are given 1 1/2 pounds of 12-12-12 or an equivalent fertilizer. The rate is increased by 1 1/2 pounds each year until 1 to 2 pounds of actual nitrogen is being applied per 1000 square feet.
Mature nut trees need about 1 to 2 pounds of actual nitrogen per 1000 square feet per year. This can be supplied by applying a lawn fertilizer or a garden fertilizer such as 12-12-12. An alternative method is to apply 5 to 6 pounds of 12-12-12 or an equivalent fertilizer per inch of trunk diameter. Check to make sure the recommended rate of of 1 to 2 pounds of actual nitrogen is being applied.
Head back branches that are too long and prune off lower branches to aid lawn mowing. Stems that form a sharp angle with the main stem should be removed as soon as possible. The tight V crotch formed by such branches is weak and susceptible to splitting.
Young trees are injured by the feeding of rodents. Rodent guards can be purchased from nurseries or mail order nurseries. Rodent guards may be made from quarter inch mesh hardware cloth. The guard must extend high enough up the tree so rodents can't stand on the snow cover to feed on the trunk. Such protection should only be needed for 5 to 7 years.
Harvesting and Storing
Nuts can be gathered when they have fallen to the ground. Dry the nuts on a screen then crack them and store them in the refrigerator or freeze them. A pound of unshelled nuts gives about a pound of nutmeats.